As one of methods for forming a metal film, there is known a method using electroless plating. As shown in FIG. 7, in the method using electroless plating in the prior art, an electroless plating solution 52 is put into a plating tank 51, and then a semiconductor wafer 54 supported by a support 53 is immersed in the electroless plating solution 52 to form a metal film.
In such a type of conventional method for forming a plating film, however, the following problems arise. As shown in FIG. 8, there arises a problem that if a plating film 63 is formed on an underlayer 61 (for example, a silicon substrate or an insulating film) through a seed layer 62, the surface of the plating film 63 comes to have unevenness. Moreover, there arises a problem that dust is generated.
In the light of the above-mentioned situation, the present invention has been made. It is therefore an object of the present invention to provide a method, for forming a plating film by electroless plating, which makes it possible to make the surface of the plating film smooth, and a device for forming such a plating film.
The inventors have found that in conventional methods of forming a film by electroless plating a smooth plating film cannot be obtained for the following reason. That is, in the case wherein an underlayer has such a nuclei (singular point) that grows abnormally, the degree of the growth of the plating film increases abnormally on the basis of the fact that the plating film increases continuously. Besides, the inventors have found that the above-mentioned singular point also causes dust. The present invention has been made on the basis of such news findings.
That is, the method of forming a plating film according to the present invention comprises the steps of providing a substrate to be treated; and performing, alternately (continuously) and repeatedly, a film-depositing step based on electroless plating and an etching step, thereby forming the plating film on a surface of the substrate.
According to the present invention, by repeating the film-depositing step based on the electroless plating and the etching step alternately, the electroless plating film can be formed while an abnormal growth region of the electroless plating film, which is caused by the singular point of the underlayer or the like, is etched. For this reason, the formed electroless plating film (in particular, the metal plating film) can be made smooth and excellent in step coverage.
In the case that the film-depositing step based on the electroless plating and the etching step are alternately repeated, the following methods may be considered: a method of putting a plating solution and an etching solution alternately into a bath holding the substrate to be treated, or a method of providing a bath in which a plating solution is put and a bath in which an etching solution is put, separately, and immersing the substrate to be treated in the baths alternately. In these methods, however, it is difficult to replace the treating solution instantaneously and carry the substrate instantaneously. In the present invention, therefore, it is preferred to deposit the electroless plating film by the following methods.
(A) In the film-depositing step, an electroless plating solution is ejected (sprayed) onto the surface of the substrate to be treated, and in the etching step, an etching solution is ejected (sprayed) onto the surface of the substrate. Concretely, it is preferred that an electroless plating solution and an etching solution are alternately ejected from the tip of the nozzle to the surface of the substrate to be treated.
(B) In the film-depositing step, the substrate to be treated is immersed in an electroless plating solution to perform the electroless plating (film-depositing step), and then the electroless plating solution used in the film-depositing step is used (in the same bath) to perform applied reverse electric bias etching.
Another method for forming a plating film according to the present invention comprises the steps of performing, repeatedly (and continuously), a film-depositing step based on electroless plating, an etching step and a washing step, thereby forming a desired plating film on a surface of the substrate to be treated.
This method is a method wherein the washing step is further added to the film-depositing step based on the electroless plating and the etching step. In this case, the formed electroless plating film can be made a smooth and continuous in the same way as in the above-mentioned method for forming the plating film according to the present invention.
In this case, there can be used a method of repeating the film-depositing step, the etching step and the washing step by ejecting (spraying) an electroless plating solution, an etching solution and a washing solution onto the surface of the substrate to be treated in the same way as in the above-mentioned method.
A device for forming a plating film according to the present invention comprises a plating solution supplying unit for supplying an electroless plating solution to a surface of a substrate to be treated, an etching solution supplying unit for supplying an etching solution to the surface of the substrate to be treated, and a control unit for repeating alternately the supply of the electroless plating solution to the surface of the substrate to be treated and the supply of the etching solution to the surface of the substrate to be treated.
Another device for forming a plating film according to the present invention comprises an electroless plating solution supplying unit for supplying a plating solution to a surface of a substrate to be treated, an etching solution supplying unit for supplying an etching solution to the surface of the substrate to be treated, a washing solution supplying unit for supplying a washing solution to the surface of the substrate to be treated, and a control unit for repeating the supply of the electroless plating solution to the surface of the substrate to be treated, the supply of the etching solution on the surface of the substrate to be treated, and the supply of the washing solution on the surface of the substrate to be treated.
A still another device for forming a plating film according to the present invention comprises a container which contains an electroless solution for subjecting electroless plating to a surface of a substrate to be treated, an etching unit in which the electroless plating solution contained in the container is used to perform applied electric bias etching on the substrate subjected to the electroless plating, and a control unit for performing, alternately and repeatedly, the electroless plating and the applied electric bias etching.
By using any one of these devices, the electroless plating film can be formed while an abnormal growth region of the electroless plating film based on the singular point of the underlayer or the like, is etched in the same way as in the above-mentioned method. For this reason, the formed electroless plating film can be made smooth and excellent in step coverage.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.